1. Field of the Invention
The present invention relates to a circuit for controlling an electric stimulus applied to an animal. In this type of system, the stimulus is usually generated by means of a collar attached to the animal's neck. The collar is typically remotely controlled by means of a radio frequency remote control. The intensity of the stimulus is variable, which allows to train the animal. The method for implementing the circuit is also detailed.
2. Description of the Related Technology
The use of electric stimuli is common in the context of animal training, and in particular that of dogs. The stimulus is applied by means of two electrodes in contact with the animal's skin and to which a high potential difference is applied.
Although it is very effective, the method has two drawbacks:                if the electrodes are not in sufficient contact with the skin because the animal's coat is obstructing, it is not possible to correctly apply the stimulus;        if, on the other hand, the electrodes are in perfect contact with the skin and the coat is damp, the stimulus is then too powerful and hurts the animal, which is not the aim sought.        
Analyzing the state of the art shows that there may be in particular a circuit and an associated method for solving the first above-mentioned problem (see document U.S. Pat. No. 6,327,999 B1). The method consists in measuring the voltage present at the electrode terminals when the stimulus is applied. If the voltage is lower than a given threshold during the application of this stimulus, the system deduces that a non-infinite impedance is connected between the electrodes and thus that the contact of the electrodes is good. If, on the other hand, the voltage is greater than that given threshold, the contact of the electrodes is considered defective.
The major drawback of this technique is that the contact of the electrodes can only be measured when the stimulus is applied. In fact, it would be more useful to check the contact of the electrodes before applying the stimulus.
The second point above has however not been resolved, also in view of the other known documents from the state of the art.
Thus, American patent U.S. Pat. No. 5,666,908 may disclose a training collar wherein a radio transmitter is used in conjunction with a microprocessor receiver incorporated into the collar for improved control of the level of the electric stimulation applied to the animal through the electrodes. A control signal including the stimulation level codes is transmitted to the receiver and the microprocessor generates series of voltage pulses whose width is determined by the stimulation level code. The generated series of pulses controls the current circulating in the transformer power circuit generating the stimulus. The peak-to-peak amplitude of the voltage pulses applied to the electrodes is determined by the width of the voltage pulses in the generated series of pulses. The number of different stimulation levels for a given voltage interval is only limited by the number of bits used to specify the above-mentioned code, which gives better control over increments in the level of stimulation applied to the animal.
American patent U.S. Pat. No. 6,170,439 B1 may disclose a training device comprising a remote transmitter and a receiver incorporated into a collar worn by an animal, in which several stimulation levels may be selected at the level of the transmitter. The information representing the desired stimulation level is transmitted to the receiver and demodulated to produce a digital signal. The microprocessor located in the receiver generates as an output a first series of pulses of constant length and with a frequency representing the selected stimulation level. This first series is filtered to produce a second series of pulses whose width represents the selected stimulation level. This second series of pulses is applied to the control electrode of the switch linked to the transformer that generates the high-voltage pulses forming the stimulus and whose intensity corresponds to the width of the pulses of the above-mentioned second series. Thus, the amplitudes of the high-voltage pulses applied to the contact electrodes represent the selected stimulation level.
American patent U.S. Pat. No. 6,184,790 B1 may disclose a device that is similar to the preceding ones, with a transformer for generating high-voltage pulses with low output impedance.